Alloy powders and coating compositions containing same

ABSTRACT

This invention relates to alloy powders suitable for thermal spraying or other cladding methods comprising an alloy of MCrAlM′ wherein M is an element selected from nickel, cobalt, iron and mixtures thereof, and M′ is an element selected from yttrium, zirconium, hafnium, ytterbium and mixtures thereof, and wherein M comprises from about 35 to about 80 weight percent of said alloy, Cr comprises from about 15 to about 45 weight percent of said alloy, Al comprises from about 5 to about 30 weight percent of said alloy, and M′ comprises from about 0.01 to about 1.0 weight percent of said alloy, said alloy powder having a mean particle size of 50 percentile point in distribution of from about 5 microns to about 100 microns.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 60/772,524, filed on Feb. 13, 2006, which is incorporated herein byreference.

FIELD OF THE INVENTION

This invention relates to alloy powders suitable for thermal spraying orother cladding methods, low thermal expansion bondcoats for thermalbarrier coatings, thermal barrier coatings comprising said bondcoats,methods for minimizing or eliminating interface stress and crackformation in a ceramic insulating layer of a thermal barrier coating,and coating compositions suitable for thermal spraying or other claddingmethods.

BACKGROUND OF THE INVENTION

Thermal barrier coatings have become essential for hot sectioncomponents in aero and IGT turbine engines, to allow them to run attodays' high temperatures. The thermal barrier coating is considered asystem, comprised of the superalloy substrate alloy, a metallic bondcoatand a zirconia-based outer ceramic layer. The zirconia ceramic hasrelatively low thermal conductivity and thus provides thermal insulationto the substrate. In the engine, the thermal barrier coating system isoperated in a temperature gradient, with the zirconia surface exposed tothe hot gas side of the turbine section and the substrate alloy of theblade, vane or combustor component typically air cooled on the backside.

Thermal expansion mismatch between the metal and ceramic layers of thethermal barrier coating will provide a varying stress in the layers asthe system is thermally cycled in service. The thermal expansion oftypical superalloys are only about 6 percent less than an MCrAlYbondcoat like LCO-22 (Co-32Ni-21Cr-8Al-0.5Y), and thermal stressesbetween them is likely to be partially relieved by plasticity. See, forexample, Alloy Reference List, United Technologies Pratt and Whitney,October 1986 and T. A. Taylor and P. N. Walsh, ICMCTF Conference, SanDiego, Apr. 28, 2003. The interface of concern is between the bondcoatand the typical zirconia ceramic. At 525° C. the thermal expansion fromroom temperature [T. A. Taylor and P. N. Walsh, supra] for these twomaterials are (mm/m): LCO-22 ZrO2-7%Y2O3 Difference (%) 7.51 5.3 42

The difference in expansion, relative to the zirconia layer is about 42percent, and this could lead to substantial interface stress, possiblycrack formation in the ceramic, if not relieved by bondcoat relaxationthrough creep. For fast thermal cycling, this stress may not be sorelieved. Since the thermal expansion of 7% yttria stabilized zirconiais already high for a ceramic material, a search for lower expansionMCrAlY bondcoats is desirable for minimizing this inter-layer stress andperhaps leading to longer thermal barrier coating thermal cycle life. Itwould therefore be desirable in the art to provide lower expansionMCrAlY bondcoats for minimizing inter-layer stress that lead to longerthermal barrier coating thermal cycle life.

SUMMARY OF THE INVENTION

This invention relates to an alloy powder suitable for thermal sprayingor other cladding methods comprising an alloy of MCrAlM′ wherein M is anelement selected from nickel, cobalt, iron and mixtures thereof, and M′is an element selected from yttrium, zirconium, hafnium, ytterbium andmixtures thereof, and wherein M comprises from about 35 to about 80weight percent of said alloy, Cr comprises from about 15 to about 45weight percent of said alloy, Al comprises from about 5 to about 30weight percent of said alloy, and M′ comprises from about 0.01 to about1.0 weight percent of said alloy, said alloy powder having a meanparticle size of 50 percentile point in distribution of from about 5microns to about 100 microns.

This invention also relates to a coating composition suitable forthermal spraying or other cladding methods comprising an alloy powder ofMCrAlM′ wherein M is an element selected from nickel, cobalt, iron andmixtures thereof, and M′ is an element selected from yttrium, zirconium,hafnium, ytterbium and mixtures thereof, and wherein M comprises fromabout 35 to about 80 weight percent of said alloy, Cr comprises fromabout 15 to about 45 weight percent of said alloy, Al comprises fromabout 5 to about 30 weight percent of said alloy, and M′ comprises fromabout 0.01 to about 1.0 weight percent of said alloy, said alloy powderhaving a mean particle size of 50 percentile point in distribution offrom about 5 microns to about 100 microns.

The invention has several advantages. For example, the low thermalexpansion of the bondcoats made from the alloy powders of this inventionminimizes or eliminates interface stress and crack formation in theceramic layer and therefore leads to longer thermal barrier coatingcycle life. There are many applications where a cast or wrought alloyhaving lower thermal expansion would allow an article to have superiorperformance. Articles fabricated from the alloy powders of thisinvention, e.g., cast or wrought alloy articles, may exhibit good hightemperature oxidation resistance, even better than typical Ni-basedsuperalloys or stainless steels, due to the high Cr and Al content ofthe alloy powders of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a graph of thermal expansion from room temperature to1075° C. for NiCrAlY coating LN-65 (pre-stabilized 4 hours/1080°C./vacuum. dilatometer, argon, 5° C./min.) showing upsweep in expansionnear 950° C., hysteresis of this effect on cooling, and slight (0.15%)additional shrinkage.

FIG. 2 depicts a graph of thermal expansion from room temperature to1075° C. for NiCrAlY coatings Alloys 3, 4 and 5 (pre-stabilized 4hours/1080° C./vacuum. dilatometer, argon, 5° C./min.).

FIG. 3 depicts a graph of sintering cycle curves for coating Alloy 3from room temperature to 1080° C., 4 hour soak at 1080° C., then coolingto room temperature; heating and cooling rates of 5° C. per minute,argon atmosphere; and length change includes thermal expansion,sintering and any phase change effects.

FIG. 4 depicts a graph of sintering cycle curves for coating LN-65 fromroom temperature to 1080° C., 4 hour soak at 1080° C., then cooling toroom temperature; heating and cooling rates of 5° C. per minute, argonatmosphere; and length change includes thermal expansion, sintering andany phase change effects.

FIG. 5 depicts a graph of sintering cycle curves for coating Alloy 5from room temperature to 1080° C., 4 hour soak at 1080° C., then coolingto room temperature; heating and cooling rates of 5° C. per minute,argon atmosphere; and length change includes thermal expansion,sintering and any phase change effects.

FIG. 6 depicts an optical micrograph (DIC) of polished and etched crosssection of Alloy 5 coating, heat treated 4 hours at 1080° C. in vacuum,then held 1 hour at 800° C. and quenched to ice water. Visible phasesinclude oxide bands, alpha-Cr, NiAl-type, gamma Ni—Cr—Al and gamma-primecolonies (Ni₃Al-type).

FIG. 7 depicts an optical micrograph (DIC) of polished and etched crosssection of Alloy 5 coating, heat treated 4 hours at 1080° C. in vacuum,then held 1 hour at 1050° C. and quenched to ice water. Visible phasesinclude oxide bands, alpha-Cr, NiAl-type and gamma Ni—Cr—Al.

FIG. 8 depicts an optical micrograph (DIC) of polished and etched crosssection of Alloy 3 coating, heat treated 4 hours at 1080° C. in vacuum,then held 1 hour at 1050° C. and quenched to ice water. Visible phasesinclude oxide bands, NiAl-type and gamma Ni—Cr—Al.

DETAILED DESCRIPTION OF THE INVENTION

As indicated above, this invention relates to alloy powders suitable forthermal spraying or other cladding methods comprising an alloy ofMCrAlM′ wherein M is an element selected from nickel, cobalt, iron andmixtures thereof, preferably nickel, and M′ is an element selected fromyttrium, zirconium, hafnium, ytterbium and mixtures thereof, preferablyyttrium, and wherein M comprises from about 35 to about 80 weightpercent of said alloy, Cr comprises from about 15 to about 45 weightpercent of said alloy, Al comprises from about 5 to about 30 weightpercent of said alloy, and M′ comprises from about 0.01 to about 1.0weight percent of said alloy, said alloy powder having a mean particlesize of 50 percentile point in distribution of from about 5 microns toabout 100 microns. The alloy powders can be coarse or fine. In anembodiment, the coarse alloy powder of this invention has a meanparticle size of 50 percentile point in distribution of from about 30microns to about 100 microns. In another embodiment, the fine alloypowder of this invention has a mean particle size of 50 percentile pointin distribution of from about 5 microns to about 50 microns.

Preferred alloy powders of this invention include those where Mcomprises from about 40 to about 70 weight percent of said alloy, Crcomprises from about 20 to about 40 weight percent of said alloy, Alcomprises from about 10 to about 25 weight percent of said alloy, and M′comprises from about 0.05 to about 0.95 weight percent of said alloy.The coarse alloy powders preferably have a mean particle size of 50percentile point in distribution of from about 40 microns to about 85microns, more preferably a mean particle size of 50 percentile point indistribution of from about 50 microns to about 60 microns. The finealloy powders preferably have a mean particle size of 50 percentilepoint in distribution of from about 10 microns to about 40 microns, morepreferably a mean particle size of 50 percentile point in distributionof from about 18 microns to about 25 microns.

An alpha-Cr phase is present in the alloys of this invention up to atemperature of at least about 1000° C. Preferably, the alpha-Cr phase ispresent in an amount sufficient to control thermal expansion of thealloys to about 6.5 mm/m or less between a temperature of from about 25°C. to about 525° C. The alloys of this invention may be heat treated tostabilize their equilibrium phases. An alpha-Cr phase is preferably inequilibrium in a thermally stabilized coating comprising the alloys ofthis invention at a temperature of about 800° C. and the alpha-Cr phasedoes not dissolve upon heating to a temperature of at least about 1000°C. The alloys of this invention fall within the gamma-beta-alpha-Crregion of a phase diagram, for example, an alpha-Cr+beta-NiAl+gamma (FCCNi alloy) phase field, at a temperature of about 1150° C.

The alloys of this invention may be prepared by conventional methodssuch as described in Superalloys II, eds. Sims, Stoloff and Hagel, JohnWiley (1987), p. 387458. The alloy powders of this invention may beprepared by conventional methods such as described in U.S. Pat. Nos.5,455,119 and 5,741,556, the disclosures of which are incorporatedherein by reference.

This invention also relates to articles produced from the alloys above,e.g., cast or wrought alloy articles, and coatings made from thepowders. The powders suitable for thermal spraying or other claddingmethods made from the alloys above may include up to about 10 volumepercent stable oxide particles. e.g., yttria, hafnia or alumina. Theinvention further relates to coatings made from the powders abovewherein, during deposition of the coating, oxygen and/or carbon areintentionally added to the coating.

As also indicated above, this invention relates to coating compositionssuitable for thermal spraying or other cladding methods comprising analloy powder of MCrAlM′ wherein M is an element selected from nickel,cobalt, iron and mixtures thereof, preferably nickel, and M′ is anelement selected from yttrium, zirconium, hafnium, ytterbium andmixtures thereof, preferably yttrium, and wherein M comprises from about35 to about 80 weight percent of said alloy, Cr comprises from about 15to about 45 weight percent of said alloy, Al comprises from about 5 toabout 30 weight percent of said alloy, and M′ comprises from about 0.01to about 1.0 weight percent of said alloy, said alloy powder having amean particle size of 50 percentile point in distribution of from about5 microns to about 100 microns. The coarse alloy powders have a meanparticle size of 50 percentile point in distribution of from about 30microns to about 100 microns, and the fine alloy powders have a meanparticle size of 50 percentile point in distribution of from about 5microns to about 50 microns.

Preferred coating compositions of this invention include alloy powderswhere M comprises from about 40 to about 70 weight percent of saidalloy, Cr comprises from about 20 to about 40 weight percent of saidalloy, Al comprises from about 10 to about 25 weight percent of saidalloy, and M′ comprises from about 0.05 to about 0.95 weight percent ofsaid alloy. The coarse alloy powders preferably have a mean particlesize of 50 percentile point in distribution of from about 40 microns toabout 85 microns, and more preferably a mean particle size of 50percentile point in distribution of from about 50 microns to about 60microns. The fine alloy powders preferably have a mean particle size of50 percentile point in distribution of from about 10 microns to about 40microns, and more preferably a mean particle size of 50 percentile pointin distribution of from about 18 microns to about 25 microns.

An alpha-Cr phase is present in the alloys of this invention up to atemperature of at least about 1000° C. Preferably, the alpha-Cr phase ispresent in an amount sufficient to control thermal expansion of thealloys to about 6.5 mm/m or less between a temperature of from about 25°C. to about 525° C. The alloys of this invention may be heat treated tostabilize their equilibrium phases. An alpha-Cr phase is preferably inequilibrium in a thermally stabilized coating comprising the alloys ofthis invention at a temperature of about 800° C. and the alpha-Cr phasedoes not dissolve upon heating to a temperature of at least about 1000°C. The alloys of this invention fall within the gamma-beta-alpha-Crregion of a phase diagram, for example, an alpha-Cr+beta-NiAl+gamma (FCCNi alloy) phase field, at a temperature of about 1150° C.

An oxide dispersion may also be included in the coating compositions ofthis invention. The oxide dispersion may be selected from alumina,thoria, yttria and rare earth oxides, hafnia and zirconia. The oxidedispersion may comprise from about 5 to about 25 volume percent of thecoating composition.

The coating compositions of this invention may be prepared byconventional methods such as described in Superalloys II, p. 459-494(powder making) and ASM Handbook, Vol. 5, Surface Engineering 1994, p.497-509 (thermal spray coatings).

This invention also relates to articles produced from the coatingcompositions above and coatings made from the powders. The powderssuitable for thermal spraying or other cladding methods made from thealloys above may include up to about 10 volume percent stable oxideparticles. e.g., yttria, hafnia or alumina. The invention furtherrelates to coatings made from the powders above wherein, duringdeposition of the coating, oxygen and/or carbon are intentionally addedto the coating.

The low thermal expansion bondcoats for thermal barrier coatings cancomprise an alloy of MCrAlM′ wherein M is an element selected fromnickel, cobalt, iron and mixtures thereof, preferably nickel, and M′ isan element selected from yttrium, zirconium, hafnium, ytterbium andmixtures thereof, preferably yttrium, and wherein M comprises from about35 to about 80 weight percent of said alloy, Cr comprises from about 15to about 45 weight percent of said alloy, Al comprises from about 5 toabout 30 weight percent of said alloy, and M′ comprises from about 0.01to about 1.0 weight percent of said alloy, said alloy thermally sprayedfrom a powder having a mean particle size of 50 percentile point indistribution of from about 5 microns to about 100 microns, said bondcoathaving a surface roughness of at least 200 micro-inches, and saidbondcoat having a thermal expansion of about 6.5 millimeters per meteror less between a temperature of from about 25° C. to about 525° C.

Preferred bondcoats include those wherein, in the composition of thealloy, M comprises from about 40 to about 70 weight percent of saidalloy, Cr comprises from about 20 to about 40 weight percent of saidalloy, Al comprises from about 10 to about 25 weight percent of saidalloy, and M′ comprises from about 0.05 to about 0.95 weight percent ofsaid alloy. In one embodiment, the alloy is sprayed from a coarse powderhaving a mean particle size of 50 percentile point in distribution offrom about 30 microns to about 100 microns, preferably a mean particlesize of 50 percentile point in distribution of from about 40 microns toabout 85 microns, and more preferably a mean particle size of 50percentile point in distribution of from about 50 microns to about 60microns. In another embodiment, the alloy is sprayed from a fine powderhaving a mean particle size of 50 percentile point in distribution offrom about 5 microns to about 50 microns, preferably a mean particlesize of 50 percentile point in distribution of from about 10 microns toabout 40 microns, and more preferably a mean particle size of 50percentile point in distribution of from about 18 microns to about 25microns.

The low thermal expansion bondcoats preferably have a surface roughnessof at least 225 micro-inches, more preferably a surface roughness of atleast 250 micro-inches. The bondcoats preferably have a thermalexpansion of about 6.25 millimeters per meter or less between atemperature of from about 25° C. to about 525° C., more preferably athermal expansion of about 6.0 millimeters per meter or less between atemperature of from about 25° C. to about 525° C. The bondcoatstypically have a thickness of from about 4 to about 480 mils, preferablya thickness of from about 80 to about 400 mils.

An alpha-Cr phase is present in the bondcoats up to a temperature of atleast about 1000° C. Preferably, the alpha-Cr phase is present in anamount sufficient to control thermal expansion of the bondcoats to about6.5 mm/m or less between a temperature of from about 25° C. to about525° C. The bondcoats may be heat treated to stabilize their equilibriumphases. An alpha-Cr phase is preferably in equilibrium in thermallystabilized bondcoats at a temperature of about 800° C. and the alpha-Crphase does not dissolve upon heating to a temperature of at least about1000° C. The bondcoats fall within the gamma-beta-alpha-Cr region of aphase diagram, for example, an alpha-Cr+beta-NiAl+gamma (FCC Ni alloy)phase field, at a temperature of about 1150° C.

An oxide dispersion may also be included in the bondcoats. The oxidedispersion may be selected from alumina, thoria, yttria and rare earthoxides, hafnia and zirconia. The oxide dispersion may comprise fromabout 5 to about 25 volume percent of the bondcoat. Articles can beproduced from the bondcoats above.

The low thermal expansion bondcoats can be deposited onto a metal ornon-metal substrate using any thermal spray device by conventionalmethods. Preferred thermal spray methods for depositing the bondcoat areinert gas shrouded plasma spraying, low pressure or vacuum plasmaspraying in chambers, high velocity oxygen-fuel torch spraying,detonation gun coating and the like. The most preferred method is inertgas shrouded plasma spraying. It could also be advantageous to heattreat the bondcoat using appropriate times and temperatures to achieve agood bond for the bondcoat to the substrate and a high sintered densityof the bondcoat. Other means of applying a uniform deposit of powder toa substrate in addition to thermal spraying include, for example,electrophoresis, electroplating and slurry deposition.

The above low thermal expansion bondcoats for thermal barrier coatingsand other related subject matter above are disclosed and claimed incopending U.S. patent application Ser. No. (D-21398-2), filed on an evendate herewith, which is incorporated herein by reference.

The bondcoat may comprise two metallic layers, both of the same ordifferent low expansion alloy composition. An inner layer bondcoat maybe made using fine powder for the thermal spray that is dense andprotective to the substrate from oxidation. An outer layer bondcoat maybe made from coarser powder to provide a rougher surface for thesubsequent attachment of the ceramic insulating layer.

The low thermal expansion bondcoats for thermal barrier coatings cancomprise (i) an inner layer comprising an inner layer alloy of MCrAlM′wherein M is an element selected from nickel, cobalt, iron and mixturesthereof, preferably nickel, and M′ is an element selected from yttrium,zirconium, hafnium, ytterbium and mixtures thereof, preferably yttrium,and wherein M comprises from about 35 to about 80 weight percent of saidinner layer alloy, Cr comprises from about 15 to about 45 weight percentof said inner layer alloy, Al comprises from about 5 to about 30 weightpercent of said inner layer alloy, and M′ comprises from about 0.01 toabout 1.0 weight percent of said inner layer alloy, said inner layeralloy thermally sprayed from a powder having a mean particle size of 50percentile point in distribution of from about 5 microns to about 50microns; and (ii) an outer layer comprising an outer layer alloy ofMCrAlM′ wherein M is an element selected from nickel, cobalt, iron andmixtures thereof, preferably nickel, and M′ is an element selected fromyttrium, zirconium, hafnium, ytterbium and mixtures thereof, preferablyyttrium, and wherein M comprises from about 35 to about 80 weightpercent of said outer layer alloy, Cr comprises from about 15 to about45 weight percent of said outer layer alloy, Al comprises from about 5to about 30 weight percent of said outer layer alloy, and M′ comprisesfrom about 0.01 to about 1.0 weight percent of said outer layer alloy,said outer layer alloy thermally sprayed from a powder having a meanparticle size of 50 percentile point in distribution of from about 30microns to about 100 microns, and said outer layer having a surfaceroughness of at least 200 micro-inches; and wherein said bondcoat has athermal expansion of about 6.5 millimeters per meter or less between atemperature of from about 25° C. to about 525° C. The inner layer alloyand the outer layer alloy may be of the same or different composition.

Preferred inner layer bondcoats include those wherein, in thecomposition of the inner layer alloy, M comprises from about 40 to about70 weight percent of said alloy, Cr comprises from about 20 to about 40weight percent of said alloy, Al comprises from about 10 to about 25weight percent of said alloy, and M′ comprises from about 0.05 to about0.95 weight percent of said alloy. The alloy is preferably sprayed froma powder having a mean particle size of 50 percentile point indistribution of from about 10 microns to about 40 microns, morepreferably a mean particle size of 50 percentile point in distributionof from about 18 microns to about 25 microns.

Preferred outer layer bondcoats include those wherein, in thecomposition of the outer layer alloy, M comprises from about 40 to about70 weight percent of said alloy, Cr comprises from about 20 to about 40weight percent of said alloy, Al comprises from about 10 to about 25weight percent of said alloy, and M′ comprises from about 0.05 to about0.95 weight percent of said alloy. The alloy is preferably sprayed froma powder having a mean particle size of 50 percentile point indistribution of from about 40 microns to about 85 microns, morepreferably a mean particle size of 50 percentile point in distributionof from about 50 microns to about 60 microns.

The outer layer bondcoats preferably have a surface roughness of atleast 225 micro-inches, more preferably a surface roughness of at least250 micro-inches. The low thermal expansion bondcoats preferably have athermal expansion of about 6.25 millimeters per meter or less between atemperature of from about 25° C. to about 525° C., more preferably athermal expansion of about 6.0 millimeters per meter or less between atemperature of from about 25° C. to about 525° C.

The inner layer bondcoats typically have a thickness of from about 4 toabout 320 mils, preferably a thickness of from about 40 to about 240mils, and more preferably a thickness of from about 80 to about 160mils. The outer layer bondcoats typically have a thickness of from about4 to about 480 mils, preferably a thickness of from about 80 to about400 mils, and more preferably a thickness of from about 160 to about 240mils.

An alpha-Cr phase is present in the bondcoats up to a temperature of atleast about 1000° C. Preferably, the alpha-Cr phase is present in anamount sufficient to control thermal expansion of the bondcoats to about6.5 mm/m or less between a temperature of from about 25° C. to about525° C. The bondcoats may be heat treated to stabilize their equilibriumphases. An alpha-Cr phase is preferably in equilibrium in thermallystabilized bondcoats at a temperature of about 800° C. and the alpha-Crphase does not dissolve upon heating to a temperature of at least about1000° C. The bondcoats fall within the gamma-beta-alpha-Cr region of aphase diagram, for example, an alpha-Cr+beta-NiAl+gamma (FCC Ni alloy)phase field, at a temperature of about 1150° C.

An oxide dispersion may also be included in the bondcoats. The oxidedispersion may be selected from alumina, thoria, yttria and rare earthoxides, hafnia and zirconia. The oxide dispersion may comprise fromabout 5 to about 25 volume percent of the bondcoat composition. Articlescan be produced from the bondcoats above.

The inner layer bondcoats can be deposited onto a metal or non-metalsubstrate and the outer layer bondcoats can be deposited onto the innerlayer bondcoats using any thermal spray device by conventional methods.Preferred thermal spray methods for depositing the bondcoats are inertgas shrouded plasma spraying, low pressure or vacuum plasma spraying inchambers, high velocity oxygen-fuel torch spraying, detonation guncoating and the like. The most preferred method is inert gas shroudedplasma spraying. It could also be advantageous to heat treat thebondcoats using appropriate times and temperatures to achieve a goodbond for the bondcoats to the substrate and a high sintered density ofthe bondcoats. Other means of applying a uniform deposit of powder to asubstrate in addition to thermal spraying include, for example,electrophoresis, electroplating and slurry deposition.

The above low thermal expansion multilayer bondcoats for thermal barriercoatings and other related subject matter above are disclosed andclaimed in copending U.S. patent application Ser. No. (D-21398-3), filedon an even date herewith, which is incorporated herein by reference.

The thermal barrier coatings for a metal or non-metal substrate cancomprise (i) a low thermal expansion bondcoat layer applied to saidsubstrate comprising an alloy of MCrAlM′ wherein M is an elementselected from nickel, cobalt, iron and mixtures thereof, preferablynickel, and M′ is an element selected from yttrium, zirconium, hafnium,ytterbium and mixtures thereof, preferably yttrium, and wherein Mcomprises from about 35 to about 80 weight percent of said alloy, Crcomprises from about 15 to about 45 weight percent of said alloy, Alcomprises from about 5 to about 30 weight percent of said alloy, and M′comprises from about 0.01 to about 1.0 weight percent of said alloy,said alloy thermally sprayed from a powder having a mean particle sizeof 50 percentile point in distribution of from about 5 microns to about100 microns, said bondcoat having a surface roughness of at least 200micro-inches, and said bondcoat having a thermal expansion of about 6.5millimeters per meter or less between a temperature of from about 25° C.to about 525° C., and (ii) a ceramic insulating layer applied to saidbondcoat layer.

Preferred bondcoat layers include those wherein, in the composition ofthe alloy, M comprises from about 40 to about 70 weight percent of saidalloy, Cr comprises from about 20 to about 40 weight percent of saidalloy, Al comprises from about 10 to about 25 weight percent of saidalloy, and M′ comprises from about 0.05 to about 0.95 weight percent ofsaid alloy. In one embodiment, the alloy is sprayed from a coarse powderhaving a mean particle size of 50 percentile point in distribution offrom about 30 microns to about 100 microns, preferably a mean particlesize of 50 percentile point in distribution of from about 40 microns toabout 85 microns, and more preferably a mean particle size of 50percentile point in distribution of from about 50 microns to about 60microns. In another embodiment, the alloy is sprayed from a fine powderhaving a mean particle size of 50 percentile point in distribution offrom about 5 microns to about 50 microns, preferably a mean particlesize of 50 percentile point in distribution of from about 10 microns toabout 40 microns, and more preferably a mean particle size of 50percentile point in distribution of from about 18 microns to about 25microns.

The low thermal expansion bondcoat layers preferably have a surfaceroughness of at least 225 micro-inches, more preferably a surfaceroughness of at least 250 micro-inches. The bondcoat layers preferablyhave a thermal expansion of about 6.25 millimeters per meter or lessbetween a temperature of from about 25° C. to about 525° C., morepreferably a thermal expansion of about 6.0 millimeters per meter orless between a temperature of from about 25° C. to about 525° C. Thebondcoat layers typically have a thickness of from about 4 to about 480mils, preferably a thickness of from about 80 to about 400 mils, andmore preferably a thickness of from about 160 to about 240 mils.

An alpha-Cr phase is present in the bondcoat layers up to a temperatureof at least about 1000° C. Preferably, the alpha-Cr phase is present inan amount sufficient to control thermal expansion of the bondcoat layerto about 6.5 mm/m or less between a temperature of from about 25° C. toabout 525° C. The bondcoat layers may be heat treated to stabilize theirequilibrium phases. An alpha-Cr phase is preferably in equilibrium inthermally stabilized bondcoat layer at a temperature of about 800° C.and the alpha-Cr phase does not dissolve upon heating to a temperatureof at least about 1000° C. The bondcoat layers fall within thegamma-beta-alpha-Cr region of a phase diagram, for example, analpha-Cr+beta-NiAl+gamma (FCC Ni alloy) phase field, at a temperature ofabout 1150° C.

An oxide dispersion may also be included in the bondcoat layers. Theoxide dispersion may be selected from alumina, thoria, yttria and rareearth oxides, hafnia and zirconia. The oxide dispersion may comprisefrom about 5 to about 25 volume percent of the bondcoat layer. Articlescan be produced from the thermal barrier coatings above.

Ceramic insulating layers that can be applied to the bondcoat layer toform a thermal barrier coating are known in the art. Illustrativeceramic insulating layers comprise zirconium oxide and yttrium oxide.Preferred ceramic insulating layers include zirconia partially or fullystabilized by yttria and having a density greater than 88% of thetheoretical density with a plurality of vertical macrocrackshomogeneously dispersed throughout the ceramic insulating layer toimprove its thermal fatigue resistance. See, for example, U.S. Pat. No.5,073,433, the disclosure of which is incorporated herein by reference.Other ceramic insulating layers useful in this invention includezirconia partially or fully stabilized by yttria and having a densityfrom about 60% to 85% of the theoretical density, e.g., low densityzirconia partially or fully stabilized by yttria.

Some suitable metal substrates include, for example, nickel basesuperalloys, nickel base superalloys containing titanium, cobalt basesuperalloys, and cobalt base superalloys containing titanium.Preferably, the nickel base superalloys would contain more than 50% byweight nickel and the cobalt base superalloys would contain more than50% by weight cobalt. Illustrative non-metal substrates include, forexample, permissible silicon-containing materials.

The low thermal expansion bondcoat layer can be deposited onto a metalor non-metal substrate, and the ceramic insulating layer can bedeposited onto the bondcoat layer, using any thermal spray device byconventional methods. Preferred thermal spray methods for depositing thebondcoat layer and ceramic insulating are inert gas shrouded plasmaspraying, low pressure or vacuum plasma spraying in chambers, highvelocity oxygen-fuel torch spraying, detonation gun coating and thelike. The most preferred method is inert gas shrouded plasma spraying.It could also be advantageous to heat treat the bondcoat layer usingappropriate times and temperatures to achieve a good bond for thebondcoat layer to the substrate and a high sintered density of thebondcoat layer. Other means of applying a uniform deposit of powder to asubstrate in addition to thermal spraying include, for example,electrophoresis, electroplating and slurry deposition.

The above thermal barrier coatings employing low thermal expansionbondcoats and other related subject matter above are disclosed andclaimed in copending U.S. patent application Ser. No. (D-21398-2), filedon an even date herewith, which is incorporated herein by reference.

The thermal barrier coatings for a metal or non-metal substrate cancomprise (a) a low thermal expansion bondcoat layer applied to saidsubstrate, said bondcoat layer comprising: (i) an inner layer comprisingan inner layer alloy of MCrAlM′ wherein M is an element selected fromnickel, cobalt, iron and mixtures thereof, preferably nickel, and M′ isan element selected from yttrium, zirconium, hafnium, ytterbium andmixtures thereof, preferably yttrium, and wherein M comprises from about35 to about 80 weight percent of said inner layer alloy, Cr comprisesfrom about 15 to about 45 weight percent of said inner layer alloy, Alcomprises from about 5 to about 30 weight percent of said inner layeralloy, and M′ comprises from about 0.01 to about 1.0 weight percent ofsaid inner layer alloy, said inner layer alloy thermally sprayed from apowder having a mean particle size of 50 percentile point indistribution of from about 5 microns to about 50 microns; and (ii) anouter layer comprising an outer layer alloy of MCrAlM′ wherein M is anelement selected from nickel, cobalt, iron and mixtures thereof,preferably nickel, and M′ is an element selected from yttrium,zirconium, hafnium, ytterbium and mixtures thereof, preferably yttrium,and wherein M comprises from about 35 to about 80 weight percent of saidouter layer alloy, Cr comprises from about 15 to about 45 weight percentof said outer layer alloy, Al comprises from about 5 to about 30 weightpercent of said outer layer alloy, and M′ comprises from about 0.01 toabout 1.0 weight percent of said outer layer alloy, said outer layeralloy thermally sprayed from a powder having a mean particle size of 50percentile point in distribution of from about 30 microns to about 100microns, and said outer layer having a surface roughness of at least 200micro-inches; and wherein said bondcoat has a thermal expansion of about6.5 millimeters per meter or less between a temperature of from about25° C. to about 525° C., and (b) a ceramic insulating layer applied tosaid bondcoat layer. The inner layer alloy and the outer layer alloy maybe of the same or different composition.

Preferred inner layer bondcoats include those wherein, in thecomposition of the inner layer alloy, M comprises from about 40 to about70 weight percent of said alloy, Cr comprises from about 20 to about 40weight percent of said alloy, Al comprises from about 10 to about 25weight percent of said alloy, and M′ comprises from about 0.05 to about0.95 weight percent of said alloy. The alloy is preferably sprayed froma powder having a mean particle size of 50 percentile point indistribution of from about 10 microns to about 40 microns, morepreferably a mean particle size of 50 percentile point in distributionof from about 18 microns to about 25 microns.

Preferred outer layer bondcoats include those wherein, in thecomposition of the outer layer alloy, M comprises from about 40 to about70 weight percent of said alloy, Cr comprises from about 20 to about 40weight percent of said alloy, Al comprises from about 10 to about 25weight percent of said alloy, and M′ comprises from about 0.05 to about0.95 weight percent of said alloy. The alloy is preferably sprayed froma powder having a mean particle size of 50 percentile point indistribution of from about 40 microns to about 85 microns, morepreferably a mean particle size of 50 percentile point in distributionof from about 50 microns to about 60 microns.

The outer layer bondcoats preferably have a surface roughness of atleast 225 micro-inches, more preferably a surface roughness of at least250 micro-inches. The low thermal expansion bondcoats preferably have athermal expansion of about 6.25 millimeters per meter or less between atemperature of from about 25° C. to about 525° C., more preferably athermal expansion of about 6.0 millimeters per meter or less between atemperature of from about 25° C. to about 525° C.

The inner layer bondcoats typically have a thickness of from about 4 toabout 320 mils, preferably a thickness of from about 40 to about 240mils, and more preferably a thickness of from about 80 to about 160mils. The outer layer bondcoats typically have a thickness of from about4 to about 480 mils, preferably a thickness of from about 80 to about400 mils, and more preferably a thickness of from about 160 to about 240mils.

An alpha-Cr phase is present in the bondcoats up to a temperature of atleast about 1000° C. Preferably, the alpha-Cr phase is present in anamount sufficient to control thermal expansion of the bondcoats to about6.5 mm/m or less between a temperature of from about 25° C. to about525° C. The bondcoats may be heat treated to stabilize their equilibriumphases. An alpha-Cr phase is preferably in equilibrium in thermallystabilized bondcoats at a temperature of about 800° C. and the alpha-Crphase does not dissolve upon heating to a temperature of at least about1000° C. The bondcoats fall within the gamma-beta-alpha-Cr region of aphase diagram, for example, an alpha-Cr+beta-NiAl+gamma (FCC Ni alloy)phase field, at a temperature of about 1150° C.

An oxide dispersion may also be included in the bondcoats. The oxidedispersion may be selected from alumina, thoria, yttria and rare earthoxides, hafnia and zirconia. The oxide dispersion may comprise fromabout 5 to about 25 volume percent of the bondcoat composition. Articlescan be produced from the thermal barrier coatings above.

Ceramic insulating layers that can be applied to the bondcoat layer toform a thermal barrier coating are known in the art. Illustrativeceramic insulating layers comprise zirconium oxide and yttrium oxide.Preferred ceramic insulating layers include zirconia partially or fullystabilized by yttria and having a density greater than 88% of thetheoretical density with a plurality of vertical macrocrackshomogeneously dispersed throughout the ceramic insulating layer toimprove its thermal fatigue resistance. See, for example, U.S. Pat. No.5,073,433, the disclosure of which is incorporated herein by reference.Other ceramic insulating layers useful in this invention includezirconia partially or fully stabilized by yttria and having a densityfrom about 60% to 85% of the theoretical density, e.g., low densityzirconia partially or fully stabilized by yttria.

Some suitable metal substrates include, for example, nickel basesuperalloys, nickel base superalloys containing titanium, cobalt basesuperalloys, and cobalt base superalloys containing titanium.Preferably, the nickel base superalloys would contain more than 50% byweight nickel and the cobalt base superalloys would contain more than50% by weight cobalt. Illustrative non-metal substrates include, forexample, permissible silicon-containing materials.

The low thermal expansion bondcoat layer can be deposited onto a metalor non-metal substrate, and the ceramic insulating layer can bedeposited onto the bondcoat layer, using any thermal spray device byconventional methods. Preferred thermal spray methods for depositing thebondcoat layer and ceramic insulating layer are inert gas shroudedplasma spraying, low pressure or vacuum plasma spraying in chambers,high velocity oxygen-fuel torch spraying, detonation gun coating and thelike. The most preferred method is inert gas shrouded plasma spraying.It could also be advantageous to heat treat the bondcoats usingappropriate times and temperatures to achieve a good bond for thebondcoats to the substrate and a high sintered density of the bondcoats.Other means of applying a uniform deposit of powder to a substrate inaddition to thermal spraying include, for example, electrophoresis,electroplating and slurry deposition.

The above thermal barrier coatings employing low thermal expansionmultilayer bondcoats and other related subject matter above aredisclosed and claimed in copending U.S. patent application Ser. No.(D-21398-3), filed on an even date herewith, which is incorporatedherein by reference.

A method for minimizing or eliminating interface stress and crackformation in a ceramic insulating layer of a thermal barrier coating cancomprise (i) applying a low thermal expansion bondcoat layer to a metalor non-metal substrate, said bondcoat layer comprising an alloy ofMCrAlM′ wherein M is an element selected from nickel, cobalt, iron andmixtures thereof, preferably nickel, and M′ is an element selected fromyttrium, zirconium, hafnium, ytterbium and mixtures thereof, preferablyyttrium, and wherein M comprises from about 35 to about 80 weightpercent of said alloy, Cr comprises from about 15 to about 45 weightpercent of said alloy, Al comprises from about 5 to about 30 weightpercent of said alloy, and M′ comprises from about 0.01 to about 1.0weight percent of said alloy, said alloy thermally sprayed from a powderhaving a mean particle size of 50 percentile point in distribution offrom about 5 microns to about 100 microns, said bondcoat having asurface roughness of at least 200 micro-inches, and wherein saidbondcoat layer has a thermal expansion of about 6.5 millimeters permeter or less between a temperature of from about 25° C. to about 525°C., and (ii) applying said ceramic insulating layer to said bondcoatlayer.

Preferred bondcoat layers include those wherein, in the composition ofthe alloy, M comprises from about 40 to about 70 weight percent of saidalloy, Cr comprises from about 20 to about 40 weight percent of saidalloy, Al comprises from about 10 to about 25 weight percent of saidalloy, and M′ comprises from about 0.05 to about 0.95 weight percent ofsaid alloy. In one embodiment, the alloy is sprayed from a coarse powderhaving a mean particle size of 50 percentile point in distribution offrom about 30 microns to about 100 microns, preferably a mean particlesize of 50 percentile point in distribution of from about 40 microns toabout 85 microns, and more preferably a mean particle size of 50percentile point in distribution of from about 50 microns to about 60microns. In another embodiment, the alloy is sprayed from a fine powderhaving a mean particle size of 50 percentile point in distribution offrom about 5 microns to about 50 microns, preferably a mean particlesize of 50 percentile point in distribution of from about 10 microns toabout 40 microns, and more preferably a mean particle size of 50percentile point in distribution of from about 18 microns to about 25microns.

The low thermal expansion bondcoat layers preferably have a surfaceroughness of at least 225 micro-inches, more preferably a surfaceroughness of at least 250 micro-inches. The bondcoat layers preferablyhave a thermal expansion of about 6.25 millimeters per meter or lessbetween a temperature of from about 25° C. to about 525° C., morepreferably a thermal expansion of about 6.0 millimeters per meter orless between a temperature of from about 25° C. to about 525° C. Thebondcoat layers typically have a thickness of from about 4 to about 480mils, preferably a thickness of from about 80 to about 400 mils, andmore preferably a thickness of from about 160 to about 240 mils.

An alpha-Cr phase is present in the bondcoat layers up to a temperatureof at least about 1000° C. Preferably, the alpha-Cr phase is present inan amount sufficient to control thermal expansion of the bondcoat layerto about 6.5 mm/m or less between a temperature of from about 25° C. toabout 525° C. The bondcoat layers may be heat treated to stabilize theirequilibrium phases. An alpha-Cr phase is preferably in equilibrium inthermally stabilized bondcoat layer at a temperature of about 800° C.and the alpha-Cr phase does not dissolve upon heating to a temperatureof at least about 1000° C. The bondcoat layers fall within thegamma-beta-alpha-Cr region of a phase diagram, for example, analpha-Cr+beta-NiAl+gamma (FCC Ni alloy) phase field, at a temperature ofabout 1150° C.

An oxide dispersion may also be included in the bondcoat layers. Theoxide dispersion may be selected from alumina, thoria, yttria and rareearth oxides, hafnia and zirconia. The oxide dispersion may comprisefrom about 5 to about 25 volume percent of the bondcoat layer.

Ceramic insulating layers that can be applied to the bondcoat layer toform a thermal barrier coating are known in the art. Illustrativeceramic insulating layers comprise zirconium oxide and yttrium oxide.Preferred ceramic insulating layers include zirconia partially or fullystabilized by yttria and having a density greater than 88% of thetheoretical density with a plurality of vertical macrocrackshomogeneously dispersed throughout the ceramic insulating layer toimprove its thermal fatigue resistance. See, for example, U.S. Pat. No.5,073,433, the disclosure of which is incorporated herein by reference.Other ceramic insulating layers useful in this invention includezirconia partially or fully stabilized by yttria and having a densityfrom about 60% to 85% of the theoretical density, e.g., low densityzirconia partially or fully stabilized by yttria.

Some suitable metal substrates include, for example, nickel basesuperalloys, nickel base superalloys containing titanium, cobalt basesuperalloys, and cobalt base superalloys containing titanium.Preferably, the nickel base superalloys would contain more than 50% byweight nickel and the cobalt base superalloys would contain more than50% by weight cobalt. Illustrative non-metal substrates include, forexample, permissible silicon-containing materials.

The low thermal expansion bondcoat layer can be deposited onto a metalor non-metal substrate, and the ceramic insulating layer can bedeposited onto the bondcoat layer, using any thermal spray device byconventional methods. Preferred thermal spray methods for depositing thebondcoat layer and ceramic insulating are inert gas shrouded plasmaspraying, low pressure or vacuum plasma spraying in chambers, highvelocity oxygen-fuel torch spraying, detonation gun coating and thelike. The most preferred method is inert gas shrouded plasma spraying.It could also be advantageous to heat treat the bondcoat layer usingappropriate times and temperatures to achieve a good bond for thebondcoat layer to the substrate and a high sintered density of thebondcoat layer. Other means of applying a uniform deposit of powder to asubstrate in addition to thermal spraying include, for example,electrophoresis, electroplating and slurry deposition.

The above method for minimizing or eliminating interface stress andcrack formation in a ceramic insulating layer of a thermal barriercoating and other related subject matter above are disclosed and claimedin copending U.S. patent application Ser. No. (D-21398-2), filed on aneven date herewith, which is incorporated herein by reference.

A method for minimizing or eliminating interface stress and crackformation in a ceramic insulating layer of a thermal barrier coating cancomprise (a) applying a low thermal expansion bondcoat layer to a metalor non-metal substrate, said bondcoat layer comprising: (i) an innerlayer comprising an inner layer alloy of MCrAlM′ wherein M is an elementselected from nickel, cobalt, iron and mixtures thereof, preferablynickel, and M′ is an element selected from yttrium, zirconium, hafnium,ytterbium and mixtures thereof, preferably yttrium, and wherein Mcomprises from about 35 to about 80 weight percent of said inner layeralloy, Cr comprises from about 15 to about 45 weight percent of saidinner layer alloy, Al comprises from about 5 to about 30 weight percentof said inner layer alloy, and M′ comprises from about 0.01 to about 1.0weight percent of said inner layer alloy, said inner layer alloythermally sprayed from a powder having a mean particle size of 50percentile point in distribution of from about 5 microns to about 50microns; and (ii) an outer layer comprising an outer layer alloy ofMCrAlM′ wherein M is an element selected from nickel, cobalt, iron andmixtures thereof, preferably nickel, and M′ is an element selected fromyttrium, zirconium, hafnium, ytterbium and mixtures thereof, preferablyyttrium, and wherein M comprises from about 35 to about 80 weightpercent of said outer layer alloy, Cr comprises from about 15 to about45 weight percent of said outer layer alloy, Al comprises from about 5to about 30 weight percent of said outer layer alloy, and M′ comprisesfrom about 0.01 to about 1.0 weight percent of said outer layer alloy,said outer layer alloy thermally sprayed from a powder having a meanparticle size of 50 percentile point in distribution of from about 30microns to about 100 microns, and said outer layer having a surfaceroughness of at least 200 micro-inches; and wherein said bondcoat has athermal expansion of about 6.5 millimeters per meter or less between atemperature of from about 25° C. to about 525° C., and (b) applying saidceramic insulating layer to said bondcoat layer.

The inner layer alloy and the outer layer alloy may be of the same ordifferent composition.

Preferred inner layer bondcoats include those wherein, in thecomposition of the inner layer alloy, M comprises from about 40 to about70 weight percent of said alloy, Cr comprises from about 20 to about 40weight percent of said alloy, Al comprises from about 10 to about 25weight percent of said alloy, and M′ comprises from about 0.05 to about0.95 weight percent of said alloy. The alloy is preferably sprayed froma powder having a mean particle size of 50 percentile point indistribution of from about 10 microns to about 40 microns, morepreferably a mean particle size of 50 percentile point in distributionof from about 18 microns to about 25 microns.

Preferred outer layer bondcoats include those wherein, in thecomposition of the outer layer alloy, M comprises from about 40 to about70 weight percent of said alloy, Cr comprises from about 20 to about 40weight percent of said alloy, Al comprises from about 10 to about 25weight percent of said alloy, and M′ comprises from about 0.05 to about0.95 weight percent of said alloy. The alloy is preferably sprayed froma powder having a mean particle size of 50 percentile point indistribution of from about 40 microns to about 85 microns, morepreferably a mean particle size of 50 percentile point in distributionof from about 50 microns to about 60 microns.

The outer layer bondcoats preferably have a surface roughness of atleast 225 micro-inches, more preferably a surface roughness of at least250 micro-inches. The low thermal expansion bondcoats preferably have athermal expansion of about 6.25 millimeters per meter or less between atemperature of from about 25° C. to about 525° C., more preferably athermal expansion of about 6.0 millimeters per meter or less between atemperature of from about 25° C. to about 525° C.

The inner layer bondcoats typically have a thickness of from about 4 toabout 320 mils, preferably a thickness of from about 40 to about 240mils, and more preferably a thickness of from about 80 to about 160mils. The outer layer bondcoats typically have a thickness of from about4 to about 480 mils, preferably a thickness of from about 80 to about400 mils, and more preferably a thickness of from about 160 to about 240mils.

An alpha-Cr phase is present in the bondcoats up to a temperature of atleast about 1000° C. Preferably, the alpha-Cr phase is present in anamount sufficient to control thermal expansion of the bondcoats to about6.5 mm/m or less between a temperature of from about 25° C. to about525° C. The bondcoats may be heat treated to stabilize their equilibriumphases. An alpha-Cr phase is preferably in equilibrium in thermallystabilized bondcoats at a temperature of about 800° C. and the alpha-Crphase does not dissolve upon heating to a temperature of at least about1000° C. The bondcoats fall within the gamma-beta-alpha-Cr region of aphase diagram, for example, an alpha-Cr+beta-NiAl+gamma (FCC Ni alloy)phase field, at a temperature of about 1150° C.

An oxide dispersion may also be included in the bondcoats. The oxidedispersion may be selected from alumina, thoria, yttria and rare earthoxides, hafnia and zirconia. The oxide dispersion may comprise fromabout 5 to about 25 volume percent of the bondcoat composition.

Ceramic insulating layers that can be applied to the bondcoat layer toform a thermal barrier coating are known in the art. Illustrativeceramic insulating layers comprise zirconium oxide and yttrium oxide.Preferred ceramic insulating layers include zirconia partially or fullystabilized by yttria and having a density greater than 88% of thetheoretical density with a plurality of vertical macrocrackshomogeneously dispersed throughout the ceramic insulating layer toimprove its thermal fatigue resistance. See, for example, U.S. Pat. No.5,073,433, the disclosure of which is incorporated herein by reference.Other ceramic insulating layers useful in this invention includezirconia partially or fully stabilized by yttria and having a densityfrom about 60% to 85% of the theoretical density, e.g., low densityzirconia partially or fully stabilized by yttria.

Some suitable metal substrates include, for example, nickel basesuperalloys, nickel base superalloys containing titanium, cobalt basesuperalloys, and cobalt base superalloys containing titanium.Preferably, the nickel base superalloys would contain more than 50% byweight nickel and the cobalt base superalloys would contain more than50% by weight cobalt. Illustrative non-metal substrates include, forexample, permissible silicon-containing materials.

The low thermal expansion bondcoat layer can be deposited onto a metalor non-metal substrate, and the ceramic insulating layer can bedeposited onto the bondcoat layer, using any thermal spray device byconventional methods. Preferred thermal spray methods for depositing thebondcoat layer and ceramic insulating layer are inert gas shroudedplasma spraying, low pressure or vacuum plasma spraying in chambers,high velocity oxygen-fuel torch spraying, detonation gun coating and thelike. The most preferred method is inert gas shrouded plasma spraying.It could also be advantageous to heat treat the bondcoats usingappropriate times and temperatures to achieve a good bond for thebondcoats to the substrate and a high sintered density of the bondcoats.Other means of applying a uniform deposit of powder to a substrate inaddition to thermal spraying include, for example, electrophoresis,electroplating and slurry deposition.

The above method for minimizing or eliminating interface stress andcrack formation in a ceramic insulating layer of a thermal barriercoating and other related subject matter above are disclosed and claimedin copending U.S. patent application Ser. No. (D-21398-3), filed on aneven date herewith, which is incorporated herein by reference.

Various modifications and variations of this invention will be obviousto a worker skilled in the art and it is to be understood that suchmodifications and variations are to be included within the purview ofthis application and the spirit and scope of the claims.

The following examples are provided to further describe certainembodiments of the invention. The examples are intended to beillustrative in nature and are not to be construed as limiting the scopeof the invention. Table 1 provides a listing of nominal compositions ofselected MCrAlY coatings. TABLE 1 Nominal Compositions of Coatings(Weight Percent) Coating Ni Co Cr Al Y LN-4 80 20 LN-5B 95 5 LN-11 47 2317 12.5 0.5 LN-21 48 23 20 8 0.5 LN-33 69 20 11 0.5 LN-46 53 15 19 120.5 +0.5 Mo LN-49 53 15 19 13 0.5 +0.5 Mo LCO-7 64 24 12 0.5 LCO-22 3238 21 8 0.5 LCO-22 + Al 29 38 21 11 0.5 LCO-29 75 18 7 0.5 LCO-40 63 2610 0.5 LCO-49 42 28 15 14 0.5 TM-309 42 25 23 10 0.5 NiCo electroplate57 43

EXAMPLE 1 Sample Preparation and Thermal Expansion Measurement Methods

Coatings were made by the plasma spray method using the Praxair SurfaceTechnologies (PST) model 1108 torch with the co-axial inert gas shieldprotecting the spray effluent. The coatings were deposited onto 12.5millimeter diameter aluminum tube substrates, about 150 millimeter longto a coating thickness 24-36 mils. The coated tubes were parted to 25millimeter long cylinders, then most of the aluminum substrate was boredout. The final step was to leach residual aluminum in 25% NaOH at acontrolled temperature (less than 38° C.) for about 30 minutes. The NaOHsolution does not attack the MCrAlY coating. After leaching, the coatingsample was rinsed in de-ionized (DI) water, ultrasonically rinsed in DIwater, rinsed in methanol and warm air-dried.

Several cylinders of each coating were vacuum heat treated for 4 hoursat 1080° C. One cylinder of each new alloy was analyzed for chemicalcomposition, and at least one was run in this thermally stabilized statein the thermal expansion cycle in a PST sapphire dilatometer. Thedilatometer is a vertical push-rod instrument, with three support rodsand the length-sensing central rod all cut from the same 600 millimeterlong single crystal of sapphire. The sample was loaded, the furnace tubeevacuated by a roughing pump then argon back-filled, three times. Thenthe argon flow was set to 800 cubic millimeters per second (mm³/s) forthe test cycle. The sample had a fine-gauge type K thermocouple wired intight contact to its mid-length. This provided the specimen temperatureto the data logger. The furnace control thermocouple is a separate,heavy gauge type K thermocouple. The heating cycle was separatelyprogrammed by a dedicated controller. The specimen length change wasmonitored by a lightly contacting sapphire rod connected to a linearvariable differential transformer, which is remote from the hot zone.For the work reported here, the samples were heated at 5° C. per minuteto 1100° C. and immediately cooled to room temperature at 5° C. perminute. If any residual sintering occurred, the data was not included inthis study, but the sample re-run until it was stable.

The dilatometer was calibrated by running a 25 millimeter long sample ofpure Ni, traceable to the National Institute of Standards andTechnology. The sample was run multiple times and the average heatingand cooling curves were compared to the accepted Ni expansion datapublished by Thermophysical Property Research Center. See Touloukian, etal., Thermal Expansion, Metallic Elements and Alloys, ThermophysicalProperties Research Center—Data Series, 12, Plenum, N.Y., 1976. Anydeviation was formed into a correction list which the computer appliedto all subsequent samples. All samples reported here were run at leasttwice, most three to four times. The corrected data for each coating wascompared to the average of all runs of that coating at each 100° C.increment of the computer printout. A three-sigma rule for outlier datawas tested, but most data was well within bounds and included in thefinal average expansion curve. The runs usually agreed with each otherwithin 0.3 millimeters per meter at each temperature, though some weremore divergent. It was found that the cooling curves usually had lowervariance between runs, and so they were chosen to represent theexpansion behavior of the coatings.

In this study of a range of MCrAlY compositions, it was found that theexpansion from 25 to 525° C. was correlated to the chemical compositionof the coating. The multiple correlation fit gave (millimeters permeter):Expansion(525°C.)=8.6892−0.01242*Ni−0.05255*Cr−0.00104*Al+0.0002693*Ni*Co  Equation(1)where the indicated element is entered into the equation as its weightpercent.

The reason why 525° C. was used in this discussion of expansion andmismatch stresses is that the typical MCrAlY coating has high yieldstress up to about that temperature, then begins to fall rapidly byabout 600° C., and is near zero at about 800° C. or higher. See T. A.Taylor and D. F. Bettridge, Surf. Coat. Technol. 86-87 (1996) 9-14. Thismeans that at high temperature the MCrAlY may not be able to transmit astress due to expansion mismatch to the zirconia layer because it is soweak or it readily creeps to relaxation.

Research measurements further found that as a class, NiCrAlYcompositions had statistically significant lower thermal expansion thanthe more prevalent CoNiCrAlY or NiCoCrAlY composition classes. Thecomparison of expansion values for 525° C. for LCO-22, NiCrAlY coatingLN-33, and a predicted value for a modified LN-33 (using the multiplecorrelation equation) were as follows: Thermal Expansion Between 25° C.and 525° C. (millimeters per meter) LCO-22 (32Ni—38Co—21Cr—8Al—0.5Y)7.51 LN-33 (69Ni—20Cr—11Al—0.5Y) 6.79 LN-33 mod (64Ni—23Cr—13Al—0.5Y)6.67Based on the logic of lower bondcoat expansion relative to the zirconialayer, it would appear that a composition like that of LN-33 wouldproduce less interface thermal stress than LCO-22, and maybe longerthermal barrier coating cyclic life.

However, the thermal expansion curve of LN-33 was lower than LCO-22 upto about 900° C., then the LN-33 expansion curve swept up significantlysuch that at 1000° C. and above the expansion was equal to LCO-22 orLN-11 (47Ni-23Co-17Cr-12.5Al-0.5Y). This upsweep has also been measuredin a similar composition coating, LN-65 (67Ni-22Cr-10Al-1Y). It isspeculated that the LN-33 upsweep was due to the phase transformation:α+γ→β+γ,where α is alpha Cr, γ is a Ni-base alloy, and β is essentially NiAl.All these phases have high thermal expansion except alpha-Cr. Within thecomposition range of LN-33, alpha-Cr goes into solution and NiAl isformed above about 950° C. See R. L. Dreshfield, T. P. Gabb inSuperalloys II, Wiley, N.Y., 1987, p. 566. The reason the othercompositions have the generally higher expansion throughout thetemperature range may be that alpha-Cr is either not present or isminimized by the presence of Co.

The above predictive Equation (1) for maintaining low thermal expansionwas used in an effort to discover new NiCrAlY compositions that wouldretain alpha-Cr to high temperature, and thus perhaps eliminate theexpansion upsweep as well.

New coatings were plasma sprayed with the PST model 1108 plasma torch,but in a non-shielded mode (air sprayed). One standard NiCrAlY powder(Ni-164) and three experimental alloy powders were made and prepared ascoatings. For the three experimental powders, a standard powder lot ofNi-164, made by the vacuum melt argon atomize process (predominateparticle size 60-120 microns), was blended with small amounts of pure Crand Al powders. These elemental powders had predominate particle sizesof 4-8 microns for the Al, 3-14 microns for the Cr, all measured by theMicrotrac method. The mixtures of 0.9 kilogram mass were V-blended for30 minutes. Table 2 shows the calculated compositions of the startingpowders and the analyzed composition of the Ni-164 powder. Powder Ni-164was analyzed by the inductively coupled plasma method. Alloys 3-5 powdercompositions were calculated, based on the Ni-164 analysis and the knownadditions of high purity Al and Cr. TABLE 2 Composition of StartingPowders (Weight Percent) Ni Cr Al Y Alloy 3 61.97 27.52 9.30 0.96 Alloy4 60.71 25.35 12.75 0.94 Alloy 5 58.23 27.00 13.63 0.90 Ni-164 66.9 21.89.99 1.04

The chemical analyses of the four heat treated coatings are given inTable 3. It was found that the coating made from the vacuum melted argonatomized powder was very close in composition to the original powder.However, the coatings made from the blends with added Al and Cr changedin composition. The alloy blends lost about 1 to 1.5% Al and gainedabout 1 to 3% Cr, going from powder to coating. The compositional shiftmost likely occurred in plasma spraying, but some could have occurred inthe vacuum heat treatment. It is important that these analyzed resultsapply to the cylindrical samples that were run in the thermal expansioncycle, as discussed below. All coatings were plasma sprayed in airwithout inert gas shrouding and then vacuum heat treated for 4 hours at1080° C. before chemical analysis. Coating LN-65 was made from Ni-164powder. Oxygen analyses were by the Leco combustion method. TABLE 3Compositions of Heat Treated Coatings (Weight Percent) Ni Cr Al Y OAlloy 3 61.5 28.45 8.53 0.83 1.11 Alloy 4 61.7 26.24 10.67 0.84 1.06Alloy 5 56.0 30.68 12.15 0.80 1.35 LN-65 67.3 21.12 9.94 1.02 0.19

Expansion Results

The thermal expansion curves of the thermally-stabilized coatings areshown in FIGS. 1 and 2. It is seen that the LN-65 coating hasessentially the same upsweep behavior of the similar composition LN-33shown earlier. Both the heating and cooling curves are shown in FIG. 1to demonstrate the hysteresis of the suspected phase transition near950° C. FIG. 1 also shows that LN-65 was not completely sintered to thefinal state possible at 1080° C. in 4 hours. An additional 1.5millimeters per meter (0.15%) shrinkage occurred in this first thermalexpansion run after the vacuum heat treatment. Subsequent runs on thesame sample do return the cooling curve to the initial specimen length.The three new alloy coatings are shown in FIG. 2, but only the coolingcurve for clarity. Alloys 3 and 4 show the upsweep at about 950° C. butit is not as sharp and there is less expansion at the highesttemperature of the thermal expansion run. There are similar hysteresiseffects for alloys 3 and 4 as seen in LN-65. Alloy 5 appears to haveessentially eliminated the upsweep, but there is still a slight effectat 950° C., which is reproducible for repeat thermal expansion runs ofthis alloy.

The expansion curves gave the following values at 525° C. on cooling,and are compared to the predicted values using Equation (1) above. Threeseparate tests were done for the experimental data reported. Thechemical analyses of the heat treated coatings of Table 3 were used inthe calculation. The oxygen in the analysis was taken to be combinedwith yttrium first, then aluminum due to the stabilizing heat treatmentat 1080° C., and only the residual metallic aluminum was used in thecalculation. Thermal expansion between 25° C. and 525° C. (cooling)[mm/m] Experimental Calculated Avg. Std. Dev. Eqn. (1) Alloy 3 6.50 0.126.36 Alloy 4 6.74 0.13 6.48 Alloy 5 6.42 0.13 6.31 LN-65 7.04 0.11 6.70The predictive Equation (1) above does well with the three new alloys,but the experimental data for LN-65 is higher than predicted. LN-65 is acomposition not much different than LN-33, whose expansion data agreedvery well with Equation (1).

Sintering Results

The vacuum sintering was done in a Lindberg furnace. The procedure wasto stand the coating cylinders on trays, pump down to 90 micronspressure, back-fill with argon to 900 microns and re-pump, repeatingthree times, then engage the high vacuum pumps to reach a vacuum ofabout 10⁻³ mm Hg before heating. Heating was at 25° C. per minute to300° C. for a one hour outgas hold then to 1080° C., holding for fourhours, then cooling to room temperature at initially 35° C. per minute.During the 1080° C. soak, chamber pressure was at 5×10⁻⁵ mm Hg.

The cylindrical samples were measured before and after the vacuum heattreatment for weight, length and average diameter. The changes in thesevalues relative to the as-coated sample are given in Table 4. Inaddition, each cylinder was measured for true density by the waterimmersion method (ASTM B-328-72), except that the oil-sealing step wasomitted, in case the samples would be run again in the dilatometer.Separate as-coated cylinders were also measured for density, includingthe oil impregnation step. These density changes are also given in Table4. All changes are decreases except density increases. Density increasevalues for vacuum also include one dilatometer thermal expansion cycle,room temperature to 1080° C. and return at 5° C. per minute. Effect ofthis extra cycle was found to increase density by 0.1 to 0.6 percentover vacuum heat treating only. TABLE 4 Coating Changes Due to 4 Hoursat 1080° C. Percent change from as-coated Weight Length Diameter DensityIn vacuum Alloy 3 0.60, 0.53 1.02, 1.02 1.08, 0.90  8.7 furnace Alloy 40.56 1.31 1.05 12.8 Alloy 5 0.47, 0.48 0.78, 0.69 0.62, 0.89 11.3 LN-650.31 1.80 1.96 13.5 In argon Alloy 3 0.41 0.95 0.80 — dilatometer Alloy5 0.34 1.10 0.90 10.8 LN-65 0.16 2.02 1.95 13.6

The dilatometer curves for the sintering cycle are shown in FIGS. 3, 4and 5 for LN-65 and Alloy 3 and 5 coatings. The length shrinkage fromthe dilatometer data and by separate micrometer measurements were inclose agreement. The percent diameter shrinkage measured by verniermicrometer was very close to the length shrinkage. The third dimension,coating thickness, was too small to measure accurately for shrinkage.Assuming thickness shrinkage was an equal percentage, a volume shrinkageestimate for the coatings by taking three times the length shrinkage.Estimated Percent Volume Shrinkage for 4 Hours/1080° C. Cycles VacuumFurnace Dilatometer Alloy 3 3.0 2.8 Alloy 4 3.9 — Alloy 5 2.2 3.3 LN-655.4 6.0These results and those of Table 4 show that dilatometry agrees wellwith vacuum furnace heat treatment, for final state sintering results.

The dilatometer data is now examined for the dynamic changes that occurduring the thermal cycle. The length change plots of FIGS. 3, 4 and 5show the data both as a function of time and temperature. The curvesinclude sintering, thermal expansion, phase development and phasetransition. These curves suggest some sintering length contractionoccurs before the sample reaches 1080° C., perhaps starting as low as800° C. Significant shrinkage further occurs during the 4 hour hold at1080° C. Finally the last segments of the curves show the cool-down toroom temperature.

LN-65 coating started from pre-alloyed powder so only solid statesintering occurred. Alloys 3 and 5 started from powder blends, and someof the sintering is likely due to aluminum liquid phase assistedsintering, as suggested by the shrinkage noted near 660° C., perhapsseen more clearly for Alloy 3. The phase transition is apparent in thesecurves also, the sharp run-up near 1000° C. (heating) for LN-65 andAlloy 3, but absent in Alloy 5. On cooling, the rapid length drop near950° C. is again seen in LN-65 and Alloy 3. The phase transition canalso be seen in the time plots of LN-65 and Alloy 3, just beforeentering the 4 hour soak period.

Coating Phase Analysis

The polished microstructures of select coatings were examined in theoptical and scanning electron microscopes. The coatings selected wereAlloy 3 and Alloy 5. In each case, separate cylinder samples were firstvacuum heat treated 4 hours at 1080° C. Then segments of the cylinderswere stabilized at 800° C. and at 1050° C. (below and above thesuspected phase transition). The stabilization time was one hour inflowing argon, followed by a rapid quench into stirred ice water. Thedilatometer trace (FIG. 1) for LN-65 shows that this stabilization timeshould have been more than adequate.

The coatings were metallographically polished then electrolyticallyetched with 1 part sulfuric acid in 7 parts methanol for 1 second at 12volts DC. The examination was done first optically with bright field andDIC at 1500 times magnification, then the identity of the alpha-Cr phasein Alloy 5 was checked in the scanning electron microscope/energydispersive spectroscope.

The phases present in the three coatings were as follows: 800° C. 1050°C. Alloy 3 γ, γ′, α-Cr γ, β-NiAl Alloy 5 γ, γ′, β-NiAl, α-Cr α-Cr, β, γIn the above samples alpha-Cr was a minor phase in Alloy 3 at 800° C.,but present. In Alloy 5, alpha-Cr was a major phase at both temperaturesof stabilization. The effects of using blended powders was also seen,the phase distribution was not uniform everywhere, which would beexpected to be found in the next phase using pre-alloyed powders.

In FIGS. 6, 7 and 8, optical micrographs of the etched microstructure ofAlloy 5, at 800° C. and 1050° C. stabilization, and for Alloy 3 at 1050°C. stabilization. It is seen that alpha-Cr is not present in Alloy 3 atthe higher temperature. The phase size was estimated from these figures.When present, the phases were essentially the same size in both alloys.The alpha-Cr phase was about 0.8-1.7 microns, of rounded cubicalmorphology. The beta NiAl was about 2-4 microns in size. The gammaprime, Ni₃Al-type phase was very fine, about 0.25-0.5 microns, andarranged in colonies, very similar to that in superalloys. See E. W.Ross and C. T. Sims in Superalloys II, Wiley, N.Y., 1987, p. 124.

In development of new NiCrAlY composition coatings, looking for means toreduce the thermal expansion of the alloy and to avoid the typicalNiCrAlY upsweep in thermal expansion at 950° C., several results wereobtained. While it proved expeditious to use pure Cr and Al additions toa pre-alloyed NiCrAlY stock powder, there were certain undesirableeffects. The chemical composition did shift somewhat from the blendedcomposition to the final coating. Mainly aluminum was lost, but chromiumgained. Alloy 5 still retained enough additional Cr and Al to test thetheory that a composition retaining alpha-Cr to high temperature wasneeded to eliminate the expansion upsweep found in LN-65 and LN-33.Air-spray deposition did oxidize the coatings somewhat, but with theminimal aluminum lost to form alumina, the residual metallic compositionstill formed the desired phases in Alloy 5.

The phase analysis of the coatings proved the usefulness of differentialinterference contrast to image the gamma-prime phase (Ni₃Al), which wasnot seen in bright field. The phases found in Alloys 3 and 5 aredifferent from those indicated for LN-33, including, in addition,gamma-prime. This is because the new compositions are richer in Cr andAl and have clearly moved to a new equilibrium phase field.

The dilatometer has proven to be very useful in this study of dynamicphase transitions and of sintering. It also gave the direct measure ofthe lower thermal expansion values for Alloy 5, which would lead to lessthermal mismatch stress at a zirconia interface with such a newbondcoat. Similar to the opening comparison of expansion differencesbetween LCO-22 and 7% yttria stabilized zirconia, the new Alloy 5 hasthe following expansion comparison, from 25° C. to 525° C. (millimetersper meter): Alloy 5 ZrO2-7%Y2O3 Difference (%) 6.42 5.3 21Thus the expansion mismatch at 525° C. was reduced by half, compared toa current standard composition bondcoat.

When pre-alloyed powder and shrouded plasma are used, both the chemicalshifts and oxide formation found in these examples should be eliminated.Thermal cycle testing of these thermal barrier coating systems based onthe new bondcoat composition, in comparison to earlier NiCoCrAlYbondcoats, should show longer life for the thermal barrier coatingsystem using the newly discovered bondcoat alloys.

The plasma spray torch in air atmosphere is not the only method ofcoating fabrication that could use the new alloys. Plasma spraying witha coaxial inert gas shroud, plasma spraying in a vacuum chamber, highvelocity oxy-fuel spraying, detonation gun spraying and laser claddingare all coating methods applicable to making the new coatings.

The comparative thermal expansion data for the yttria-stabilizedzirconia coatings were also made by the plasma spray process. However,the new alloys can also be overcoated by oxide ceramics made by otherprocesses, such as electron beam physical vapor deposition, liquidsolution-based plasma deposition, high velocity oxy-fuel deposition, anddetonation gun deposition, among others. The benefits of the new lowexpansion bondcoat will be found independent of the deposition method ofthe zirconia-based ceramic top layer.

In addition to new low expansion coating alloys of this invention, solidarticles may also be fabricated that could benefit from low expansion.As in the example above, consider the comparison of thermal expansionfrom 25° C. to 525° C. of a typical superalloy and Alloy 5 (millimetersper meter). Typical Ni Superalloy Alloy 5 7.4 6.42The new NiCrAlY Alloy 5 was thus found to have lower thermal expansionthan even a typical Ni-based superalloy. There are likely manyapplications where a cast or wrought alloy having lower thermalexpansion would allow an article to have superior performance. Anarticle of composition based on Alloy 5 or near compositions, shouldhave excellent high temperature oxidation resistance, better than mosttypical Ni-based superalloys or stainless steels, due to the high Cr andAl content of these new NiCrAlY alloys.

Powder particle size distribution is measured by the light scatteringmethod with the powder sample suspended in a liquid solution (ASTM B822-97) using a Microtrac model X-100 instrument (Leeds & Northrup, St.Petersburg, Fla.) operated in the X-100 mode.

Coating surface roughness is measured by the contact stylus method (ASTMD 7127-05) using a Taylor Hobson model Surtronic 3P (Leicester, England)in the Ra mode.

While it has been shown and described what is considered to be certainembodiments of the invention, it will, of course, be understood thatvarious modifications and changes in form or detail can readily be madewithout departing from the spirit and scope of the invention. It is,therefore, intended that this invention not be limited to the exact formand detail herein shown and described, nor to anything less than thewhole of the invention herein disclosed and hereinafter claimed.

1. An alloy powder suitable for thermal spraying or other claddingmethods comprising an alloy of MCrAlM′ wherein M is an element selectedfrom nickel, cobalt, iron and mixtures thereof, and M′ is an elementselected from yttrium, zirconium, hafnium, ytterbium and mixturesthereof, and wherein M comprises from about 35 to about 80 weightpercent of said alloy, Cr comprises from about 15 to about 45 weightpercent of said alloy, Al comprises from about 5 to about 30 weightpercent of said alloy, and M′ comprises from about 0.01 to about 1.0weight percent of said alloy, said alloy powder having a mean particlesize of 50 percentile point in distribution of from about 5 microns toabout 100 microns.
 2. The alloy powder of claim 1 wherein M is nickeland M′ is yttrium.
 3. The alloy powder of claim 1 having a mean particlesize of 50 percentile point in distribution of from about 5 microns toabout 50 microns.
 4. The alloy powder of claim 1 wherein M comprisesfrom about 40 to about 70 weight percent of said alloy, Cr comprisesfrom about 20 to about 40 weight percent of said alloy, Al comprisesfrom about 10 to about 25 weight percent of said alloy, and M′ comprisesfrom about 0.05 to about 0.95 weight percent of said alloy.
 5. The alloypowder of claim 1 wherein an alpha-Cr phase is present up to atemperature of at least about 1000° C.
 6. The alloy powder of claim 1that is heat treated to stabilize equilibrium phases of said alloy. 7.The alloy powder of claim 1 wherein an alpha-Cr phase is in equilibriumin a thermally stabilized coating comprising said alloy at a temperatureof about 800° C. and said alpha-Cr phase does not dissolve upon heatingto a temperature of at least about 1000° C.
 8. The alloy powder of claim1 that falls within an alpha-Cr+beta-NiAl+gamma (FCC Ni alloy) phasefield at a temperature of about 1150° C.
 9. A metal or non-metalsubstrate coated with the alloy powder of claim
 1. 10. The alloy powderof claim 1 with the addition of up to about 10 volume percent stableoxide particles.
 11. The alloy powder of claim 1 wherein the stableoxide particles are selected from yttria, hafnia or alumina.
 12. Acoating made from the alloy powder of claim
 1. 13. A coating made fromthe alloy powder of claim 1 wherein, during deposition of the coating,oxygen and/or carbon are intentionally added to the coating.
 14. A castor wrought alloy article made from the alloy powder of claim
 1. 15. Acoating composition suitable for thermal spraying or other claddingmethods comprising an alloy powder of MCrAlM′ wherein M is an elementselected from nickel, cobalt, iron and mixtures thereof, and M′ is anelement selected from yttrium, zirconium, hafnium, ytterbium andmixtures thereof, and wherein M comprises from about 35 to about 80weight percent of said alloy, Cr comprises from about 15 to about 45weight percent of said alloy, Al comprises from about 5 to about 30weight percent of said alloy, and M′ comprises from about 0.01 to about1.0 weight percent of said alloy, said alloy powder having a meanparticle size of 50 percentile point in distribution of from about 5microns to about 100 microns.
 16. The coating composition of claim 15wherein M is nickel and M′ is yttrium.
 17. The coating composition ofclaim 15 wherein said alloy powder has a mean particle size of 50percentile point in distribution of from about 5 microns to about 50microns.
 18. The coating composition of claim 15 wherein M comprisesfrom about 40 to about 70 weight percent of said alloy, Cr comprisesfrom about 20 to about 40 weight percent of said alloy, Al comprisesfrom about 10 to about 25 weight percent of said alloy, and M′ comprisesfrom about 0.05 to about 0.95 weight percent of said alloy.
 19. Thecoating composition of claim 15 wherein an alpha-Cr phase is present upto a temperature of at least about 1000° C.
 20. The coating compositionof claim 15 that is heat treated to stabilize equilibrium phases of saidcoating composition.
 21. The coating composition of claim 15 wherein analpha-Cr phase is in equilibrium in said coating composition that hasbeen thermally stabilized at a temperature of about 800° C. and saidalpha-Cr phase does not dissolve upon heating to a temperature of atleast about 1000° C.
 22. The coating composition of claim 15 that fallswithin an alpha-Cr+beta-NiAl+gamma (FCC Ni alloy) phase field at atemperature of about 1150° C.
 23. The coating composition of claim 15further comprising an oxide dispersion.
 24. The coating composition ofclaim 15 wherein the oxide dispersion is selected from alumina, thoria,yttria and rare earth oxides, hafnia and zirconia.
 25. The coatingcomposition of claim 15 wherein the oxide dispersion comprises fromabout 5 to about 25 volume percent of said coating composition.
 26. Acoating made from the coating composition of claim
 15. 27. A coatingmade from the coating composition of claim 15 wherein, during depositionof the coating, oxygen and/or carbon are intentionally added to thecoating.
 28. A metal or non-metal substrate coated with the coatingcomposition of claim 15.